Method of forming monolithic cmos-mems hybrid integrated, packaged structures

ABSTRACT

A method of forming Monolithic CMOS-MEMS hybrid integrated, packaged structures includes the steps of providing: providing a semiconductor substrate with pre-fabricated cmos circuits on the front side and a polished back-side with through substrate conductive vias; forming at least one opening in the polished backside of the semiconductor substrate by appropriately protecting the front-side; applying at least one filler material in the at least one opening on the semiconductor substrate; positioning at least one prefabricated mems, nems or cmos chip on the filler material, the chip including a front face and a bare back face with the prefabricated mems/nems chips containing mechanical and dielectric layers; applying at least one planarization layer overlying the substrate, filler material and the chip; forming at least one via opening on a portion of the planarization layer interfacing pads on the chip and the through substrate conductive vias; applying at least one metallization layer overlying the planarization layer on the substrate and the chip connecting the through substrate conductive vias to the at least one chip; applying at least one second insulating layer overlying the metallization layer; performing at least one micro/nano fabrication etching step to release the mechanical layer on the prefabricated mems/nems chips; positioning protective cap to package the integrated device over the mems/nems device area on the pre-fabricated chips.

RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 12/497,107 filed Jul. 2, 2009 and U.S. patentapplication Ser. No. 12/732,689 filed Mar. 26, 2010 which areincorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a method for integrating MEMS and CMOSstructures.

BACKGROUND OF THE INVENTION

Monolithic integration of MEMS/NEMS and electronics offers significantbenefits enabling high volume production driving down the per-unit costsof sensor and actuator systems significantly. Micromechanical transducersystems not only need to receive analog and digital electrical inputsand transmit the output, but should also be able to measure rotation,strain, temperature, pressure, acceleration, infrared radiation, microfluidic chemical properties of liquids and gasses. Effective integrationoffers other benefits, including, simplifying interconnect issues,reduced packaging and fabrication complexity and significantly improvingthe overall performance and ease of use for the device.

One method of monolithic integration of CMOS and MEMS is to modify thecomplementary metal-oxide semiconductor (CMOS) foundry facility tofabricate micromechanical structures. Some of the commonly usedmicromechanical (MEMS) mechanical structures like polysilicon, nitrideetc require high-temperature processing during deposition and annealingto relieve stress and this cannot be performed on the same substrate inthe presence of CMOS electronics due to the lower temperature limitationof the metals in CMOS. Another limitation of the method is that CMOSrequires the substrate to be planar after the MEMS fabrication toachieve high-resolution features in the photolithographic process. Thus,the current CMOS-MEMS integration methodologies faces seriouslimitations, requiring sacrificing materials and allowing very littleflexibility in device design.

Monolithic integration process may be divided into three classes: (1)Pre CMOS (2) Intermediate CMOS (3) Post CMOS. In prior art “pre CMOS”fabrication process methods, MEMS/NEMS structures are fabricated beforethe electronics are integrated. One example of this process is themicromechanics-first approach developed at Sandia National Laboratory byJ. Smith et al. In this process a pre-etched trench is used to house theMEMS structures. After the fabrication of the desired MEMS structures,this housing is refilled with oxide, planarized usingchemical-mechanical polishing (CMP), and finally sealed with a nitridemembrane. Conventional CMOS processing was then carried out next to thisMEMS area. This defined a CMOS device area and micromechanical devicearea on the same substrate as shown in FIG. 1. One of the disadvantageswith this process is that it needs a dedicated production line and theprocess is complicated.

In the Intermediate CMOS fabrication process, the process flow betweenCMOS and MEMS is mixed in the sequence. Initially a part of the CMOSprocess is performed and then paused for additional thin film depositionor micromachining steps. Some of the commercially available sensors inthis art include the Analog Devices integrated MEMS and Infineon'spressure sensor shown by C. Hierold. In the post CMOS process, MEMS/NEMSstructures are fabricated after the CMOS or electronics is fabricated onthe substrate. The disadvantage of this process is the temperaturelimitation of the process to below 400° C. to protect the aluminum inthe electronics. This leads to the elimination of commonly usedMEMS/NEMS high temperature materials like LPCVD polysilicon, siliconnitride etc.

An alternative approach to integration and packaging using high densityinterconnect (HDI) multichip modules (MCMs) was developed by researchersat GE Corporate Research and Development center as a “chips first”approach described in by W. Daum et al. as shown in FIG. 2. This processinvolves placing bare chips of MEMS test die and a generic CMOSelectronics die into mechanically milled cavities on a base substrateand then fabricating the thin-film interconnect structure on top of thecomponents. A computer-controlled argon ion laser system drills viaholes through the polyimide film directly to the chip I/O pads. Theinterconnection metallization and via contacts were formed by a combinedsputtering/electroplating process and patterned by computer-controlledadaptive laser lithography and etching. Some of the limitations withthis process were the warping of the MEMS device due to excessiveheating during the laser ablation step.

Prior art monolithic integration processes in this art involve utilizingcomplimentary metal-oxide semiconductor (CMOS) semiconductor layers tofabricate micromechanical structures is shown in U.S. Pat. No.5,717,631, U.S. patent application Ser. No. 11/602,087, U.S. Pat. No.6,060,336. Some of the major limitations with this approach involve theneed to sacrifice MEMS/NEMS materials with various mechanical propertiesas commercial foundries cannot modify their processes to suit MEMS/NEMS.This also adds additional constraints when fabricating the MEMS/NEMSsensors or actuators as they would need to limit their processingtechniques like etching, deposition so as to not harm the electroniccircuits present on the substrate. Stress and other mechanicaldeficiencies may lead to device failure when the materials tailored toCMOS are modified as mechanical elements in MEMS.

Prior art hybrid MCM technology processes include putting one or severaldies with different functionality into prefabricated trenches on asubstrate, planarizing these chips, providing an insulator layer on topand forming electrodes have been demonstrated in U.S. Pat. No.6,403,463, U.S. Pat. No. 6,780,696 B1, U.S. Pat. No. 6,154,366, U.S.Pat. No. 6,759,270. Some of the major drawbacks in these prior artreferences include semiconductor substrates like silicon that arefragile and the devices need to be repackaged resulting in significantcosts.

The invention describes a method of manufacture for Monolithic hybridintegration of CMOS-MEMS with enhanced flexibility of using materialswithout hindrance to process parameters. This invention enables thisintegration effectively without the need to sacrifice the inherentstrengths of both the CMOS or MEMS technologies and bringing about theirfusion in a hybrid approach on a common substrate. This invention alsoallows the ability to effectively package the entire system afterintegration.

Several of the limitations mentioned above are overcome in the presentinvention which describes a method to effectively synergizeCMOS-MEMS/NEMS functionality and finally package them creating a verycost effective, reliable, robust transduction system In the presentinvention, protective layers are coated on the substrate to protecteither the CMOS device area in the “Post CMOS” process or the MEMSdevice area in the “Pre CMOS” process to prevent damage to the sensor orelectronics. Oxygen plasma etching can be used to open the vias toaccess conductive layers, being precisely defined by photolithographyinstead of laser which is known to cause damage in some of the previousintegration approaches.

Either the “Post CMOS” or “Pre CMOS” fabrication may be carried out on asemiconductor substrate without compromising on the individualtechnologies strength and then integrating CMOS if MEMS is alreadypresent or MEMS if CMOS is already present on the same substrate.

The invention provides an improved ability to effectively package anentire system using a glass, silicon, plastic or metal housing.Packaging provides physical protection against external scratching andbreakage, environmental protection and any other external forces thatmay damage the leads or the sensors. Effective packaging of theintegrated system leads to lower cost, improved reliability and improvedperformance. This invention addresses some of the important issuespresent in current packaging methodologies. As one specific examplerelated to reliability issues with plastic packages, the Thermalcoefficient of expansion (TCE) mismatch resulting from the curing of theresins as they shrink in volume, creates a large temperaturedifferential resulting in large strain mismatch, damaging the wirebonds. This issue can be eliminated or reduced significantly in thepresent invention as there will be no wire bonds involved and thefabrication is planar and the metal traces can be more effectivelyprotected. The packaging methodology from the current invention alsoeliminates the need for solder bumps for integration of CMOS-MEMS andpackaging. The invention also provides a method to further encapsulatethe entire system by adding a secondary protective layer of organicmaterials providing a very effective packaging methodology.

As the use of miniaturized sensing becomes widespread, the need forlarge sensing arrays becomes a necessity for increased performance andhence there is an urgent need for such a system with propertiesincluding robust integration yet easy manufacturability and the interestfor such a technology has significantly risen in the past few years.Existing technologies use wire or flip-chip bonding to perform thisintegration and are limited because with the increase in the number ofarrays, wire bonding becomes extremely complicated due to the increasein wires and since the sensing area should preferably be on top surfaceflip chip bonding is restricted. The invention describes a method ofmanufacture for heterogeneous integration of CMOS-MEMS in a 3D approachwith enhanced flexibility of using materials without hindrance toprocess parameters. This invention enables this integration effectivelywithout the need to sacrifice the inherent strengths of both the CMOS orMEMS technologies and bringing about their fusion in a hybrid approachon a common substrate. This invention also allows the ability toeffectively package the entire system after integration.

SUMMARY OF THE INVENTION

Accordingly, the invention relates to a method of forming heterogeneousCMOS-MEMS hybrid integrated structures. In one aspect, the methodincludes the steps of: providing a semiconductor substrate withselection from pre fabricated cmos circuits, mems, nems materials on thefront side and a polished backside area available for post-cmos,micro/nano fabrication with through substrate conductive vias and theprefabricated mems or nems materials containing mechanical anddielectric layers; forming at least one opening in the polished backsideof the semiconductor substrate by appropriately protecting thefront-side; applying at least one filler material in the at least oneopening on the semiconductor substrate; positioning at least oneprefabricated mems, nems or cmos chip on the filler material, the chipincluding a front face and a bare back face with the filler materialenabling the chip to be anchored and planar to the substrate; applyingat least one planarization layer overlying the substrate, fillermaterial and the chip; forming at least one via opening on a portion ofthe planarization layer interfacing pads on the chip and the throughsubstrate conductive vias; applying at least one metallization layeroverlying the planarization layer on the substrate and the chipelectrically connecting the through substrate conductive vias to the atleast one chip; applying at least one second insulating layer overlyingthe metallization layer; performing at least one micro/nano fabricationetching step to release the mechanical layer.

In another aspect, the method includes the steps of: providing asemiconductor substrate with pre-fabricated cmos circuits on the frontside and a polished back-side with through substrate conductive vias;forming at least one opening in the polished backside of thesemiconductor substrate by appropriately protecting the front-side;applying at least one filler material in the at least one opening on thesemiconductor substrate; positioning at least one prefabricated mems,nems or cmos chip on the filler material, the chip including a frontface and a bare back face with the prefabricated mems/nems chipscontaining mechanical and dielectric layers; applying at least oneplanarization layer overlying the substrate, filler material and thechip; forming at least one via opening on a portion of the planarizationlayer interfacing pads on the chip and the through substrate conductivevias; applying at least one metallization layer overlying theplanarization layer on the substrate and the chip connecting the throughsubstrate conductive vias to the at least one chip; applying at leastone second insulating layer overlying the metallization layer;performing at least one micro/nano fabrication etching step to releasethe mechanical layer on the prefabricated mems/nems chips; positioningprotective cap to package the integrated device over the mems/nemsdevice area on the pre-fabricated chips.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Prior Art showing cross-section of the embedded micromechanicsapproach to CMOS/MEMS integration from Sandia National labs;

FIG. 2 Prior Art showing simplified cross-sectional view of HDIinterconnect MCM technology from GE;

FIG. 3 a-3 h is a cross-sectional view showing the process flow forbuilding a “post CMOS” monolithic CMOS-MEMS hybrid integration systemand packaging;

FIG. 4 a-FIG. 4 f is a cross-sectional view showing the process flow forbuilding a “pre CMOS” monolithic CMOS-MEMS hybrid integration system;

FIGS. 4( g 1-g 4) is a cross-sectional view showing the post fabricationof the integrated CMOS MEMS realizing a suspended structure usingisotropic etching and finally packaged;

FIGS. 4( h 1-h 5) is a cross-sectional view showing the post fabricationof the integrated CMOS MEMS realizing anisotropic etching in the frontand backside and finally packaged;

FIG. 5 a-FIG. 5 f is a cross-sectional view showing the process flow forbuilding a monolithic CMOS-MEMS hybrid integrated polysiliconpiezoresistive strain gage system;

FIG. 6. is a micrograph showing the MEMS polysilicon strain gageconnected to the AD621 instrumentation amplifier using electroplated,evaporated Au forming a integrated system;

FIG. 7 is a micrograph showing the metallization created to form thewheatstone bridge using the MEMS based polysilicon piezoresistors;

FIG. 8 is a micrograph showing the metallization connecting the Ad621instrumentation amplifier to the output pads for external stimuli.

FIG. 9 shows the plot for the input voltage stimuli vs. the outputvoltage response for the integrated piezoresistive strain gage systemwithout any applied forces;

FIG. 10 is a cross-sectional view for the 3D CMOS MEMS/NEMS integration;

FIG. 11 is a cross-sectional view for an alternative embodiment of 3DCMOS MEMS/NEMS integration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the various Figures there is shown an effective, reliable,and relatively low cost method of integration between CMOS-MEMS/NEMS.

In one embodiment of a “post CMOS” or “CMOS first” hybrid integrationapproach shown in FIGS. 3 a-3 h, the already fabricated CMOSsemiconductor substrate is modified to achieve this integration. TheCMOS device area is first protected so as not to affect theirfunctionality in the ensuing process; fabrication is continued on thesame substrate and integrated by coupling the micromechanical structuresin a hybrid approach by placing the MEMS/NEMS dies that have been diced.The integrated system is finally packaged in an effective manner.

Again referring to FIGS. 3 a-h, there is shown a cross-sectional processflow for the “Post CMOS” monolithic hybrid integration approach on asemiconductor substrate 302. A CMOS fabricated semiconductor substrate302 with dielectric layers and metallization in FIG. 3 a is provided asa starting point in the integration process. The CMOS device area 304may include digital logic circuits, operational amplifiers, inverters,analog and digital circuitry, digital switches, voltage comparatorswhich enable the sensors and actuators to receive analog and digitalsignals for their effective operation.

Next, as shown in FIG. 3 b, a protective layer 306 may be applied to theCMOS semiconductor substrate 302 by either spin coated or deposited invacuum to protect the CMOS area 304 from further processing steps.Protective layer 306 may be selected from oxides, nitrides, polymers, ortheir combination having a thickness of sub-microns to several micronsand that which can effectively protect the electronics. The protectivelayer 306 may be selectively patterned using lithography and etchedanisotropically using oxygen plasma RIE for materials such as polyimideand parylene to define a trench 308 outside of the CMOS device area 304.The trench 308 may be etched using DRIE Bosch process and may belithographically defined by the size of a chip 312. The protective layer306 may be left behind or removed.

In a following step, as shown in FIG. 3 c, a filler layer 310 may bedeposited or dispensed into the trench 308 to anchor a chip 312 into thetrench 308 and also to fill a gap between the chip 312 and the wall ofthe trench 308 and will also ensure the planarity of the chip 312 to thesubstrate 302. The filler material 310 may be selected from oxides,polyimides, silicones, epoxiess, or their combination or any othermaterials with similar properties.

In a next step as shown in FIG. 3 d, the chip 312 of CMOS, MEMS/NEMS ora combination of them may be placed in the trench 308. As describedabove, a CMOS integrated chip may include voltage comparators, diodes,op-amps, or other electronic components like power management circuits,resistors, capacitors, and inductors. A MEMS/NEMS dies may include butare not limited to accelerometers, resonators, micro-gyroscopes,microphones, micro-bolometers, transducers involving chemical andbiological, optical, mechanical, radiation, thermal, capacitive,rotation, strain, magnetic and electromagnetic, flow, and micro-fluidicchemical properties of liquids and gases.

In a following step as shown in FIG. 3 e, a first insulating layer 314may be deposited covering the front face and/or the sides of the chip312 providing the continuity from the semiconductor substrate 302 to thechip 312. The first insulating layer 314 may be selected from polymers,oxides, nitrides, glass, quartz polyimide, parylene, silicone, or acombination of the above. At least one via opening 316 may be etchedthrough the first insulation layer 314 to make electrical contact. Thefirst insulation layer 314 may be anisotropically etched using oxygenplasma or may be etched using wet or dry etching.

In a next step as shown in FIG. 3 f, a metallization layer 318 may beapplied to connect the CMOS area 304 on the semiconductor substrate 302to the chip 312 which may include a contact area having an input/outputpad or bond area to make electrical contact. The metallization layer 318may be selected from metals such as, aluminum, copper, titanium, chrome,gold, silver, iridium or their combination that can be evaporated,sputtered or electroplated. A second insulating layer 320 may bedeposited overlying the CMOS area 304 on the semiconductor substrate 302covering the via 316 and overlying the metallization layer 318 on thechip 312. The second insulation layer 320 may be selected from polymersincluding polyimide, parylene, silicones, oxides, nitrides, glass,quartz or their combination. A person of ordinary skill in this art willbe able to easily make further alterations and modifications inpackaging after reading the present invention. It can easily be inferredthat any particular embodiment illustrated with diagrams and explainedcannot be considered limiting. For example the metallization layer 318may include multiple layers sandwiched between multiple insulatinglayers 320 connecting multiple devices and/or multiple chips on thesubstrate.

In a next step as shown in FIG. 3 g, the packaging of the integrateddevice is detailed. The packaging of the device may include aligning arigid substrate 322 and bonding it to the substrate 302 by using aninterfacial material 324. The packaging substrate 322 may be selectedfrom ceramics, thermoplastics, thermosets, glass, silicon, quartz,plastic or metals. The bonding may be anodic, eutectic, solder, polymeror fusion bonding. The interfacial material 324 may be selected frommetal and/or alloys like gold, tin, epoxies like Benzocyclobuten (BCB)and SU8.

In a subsequent step as shown in FIG. 3 h, a secondary protective layer326 may be applied overlying the rigid substrate 322. The secondaryprotective layer 326 may be selected from polymers, oxides, nitrides,metals or a combination of them. A person of ordinary skill in this artwill be able to easily make further alterations and modifications inpackaging after reading the present invention.

A second embodiment of a “Pre CMOS” monolithic hybrid integrationapproach is shown in FIG. 4. The second embodiment may includemicromachined micromechanical systems involving high temperaturematerials including but not limited to LPCVD oxide, nitride andpolysilicon to effectively fabricate transducers including but notlimited to accelerometers, resonators, micro-gyroscopes, microphones,micro-bolometers, etc. A protective layer may be coated on the MEMSdevice area on the substrate to protect them from further fabricationsteps that will be carried out on the same substrate. This protectivelayer protects the MEMS device area from the ensuing chemical etching.The CMOS electronics dies or any other MEMS/NEMS chips may be placed ina photolithographically etched trench with the help of a filler materialand then connected to the already fabricated portion of the MEMS/NEMSdevice area with metallization evaporated or sputtered. The CMOS orelectronic dies also involve more sophisticated circuits includingdigital interfaces and micro controllers. Thus the temperaturelimitation of the process to below 400° C. to protect the aluminum inthe electronics, which has been the limiting step in some of the currentintegration methodologies, can now be overcome with the presentinvention with the potential to realize several novel devices.Processing can further resume on the MEMS device area by protecting theCMOS and or MEMS/NEMS chip areas and the MEMS/NEMS device area torealize a released structural layer and any other requirement dependingon a specific application. It should be realized that a person ofordinary skill in this art will be able to make further alterations andmodifications.

FIG. 4 illustrates a cross-sectional process flow for the “Pre CMOS”monolithic hybrid integration approach on a substrate 402.

Referring to FIG. 4 a there is shown a first step including providing asubstrate 402 that may be a semi-conductor insulator as described above.The substrate 402 may include MEMS/NEMS materials 404 applied thereon.In one aspect, the MEMS/NEMS material 404 that can be made conductiveinclude high temperature MEMS materials such as LPCVD polysilicon thatcan be later doped in boron or phosphorous and or may also include LPCVDnitride and or metals such as aluminum, copper, titanium, chrome, gold,silver, iridium or their combination that can be evaporated, sputteredor electroplated. In the illustrated embodiment, a first insulatinglayer 406 may be applied to the MEMS/NEMS materials 404.

Next, as shown in FIG. 4 b, a protective layer 408 may be applied to thesemiconductor substrate 402 by either spin coating or depositing invacuum to protect the MEMS/NEMS area 404 from further processing steps.Protective layer 408 may be selected from oxides, nitrides, polymers, ortheir combination having a thickness of sub-microns to several micronsand that which can effectively protect the electronics. The protectivelayer 408 may be selectively patterned using lithography and etchedanisotropically using oxygen plasma RIE for materials such as polyimideand parylene to define a trench 410 outside of the MEMS/NEMS area 404.The trench 410 may be etched using DRIB Bosch process and may belithographically defined by the size of chips 414. The protective layer408 may be left behind or removed.

In a following step, as shown in FIG. 4 c, a filler layer 412 may bedeposited or dispensed into the trench 410 to anchor the chip 414 intothe cavity and also to fill a gap between the chip 414 and the wall ofthe trench 410 and will also ensure the planarity of the chip 414 to thesubstrate 402. The filler material 412 may be selected from oxides,polyimides, silicones, epoxies, or their combination or any othermaterials with similar properties.

In a next step as shown in FIG. 4 d, the chip 414 of CMOS, MEMS/NEMS ora combination of them may be placed in the trench 410. As describedabove, a CMOS integrated chip may include voltage comparators, diodes,op-amps, or other electronic components like power management circuits,resistors, capacitors, and inductors. A MEMS/NEMS dies may include butare not limited to accelerometers, resonators, micro-gyroscopes,microphones, micro-bolometers, transducers involving chemical andbiological, optical, mechanical, radiation, thermal, capacitive,rotation, strain, magnetic and electromagnetic, flow, and micro-fluidicchemical properties of liquids and gases.

In a following step as shown in FIG. 4 e, a second insulating layer 416may be deposited covering the front face and/or the sides of the chip414 providing the continuity from the semiconductor substrate 402 to thechip 414. The second insulating layer 416 may be selected from polymers,oxides, nitrides, glass, quartz polyimide, parylene, silicone, or acombination of the above. At least one via opening 418 may be etchedthrough the second insulation layer 416 to make electrical contact. Thesecond insulation layer 416 may be anisotropically etched using oxygenplasma or may be etched using wet or dry etching.

In a next step as shown in FIG. 4 f, a metallization layer 420 may beapplied to connect the MEMS/NEMS on the semiconductor substrate 402 tothe chip 414 which may include a contact area having an input/output pador bond area to make electrical contact. The metallization layer 420 maybe selected from metals such as, aluminum, copper, titanium, chrome,gold, silver, iridium or their combination that can be evaporated,sputtered or electroplated. A third insulating layer 422 may bedeposited overlying the MEMS/NEMS on the semiconductor substrate 402covering the via 418 and overlying the metallization layer 420 on thechip 414. The third insulation layer 422 may be selected from polymersincluding polyimide, parylene, silicones, oxides, nitrides, glass,quartz or their combination. A person of ordinary skill in this art willbe able to easily make further alterations and modifications inpackaging after reading the present invention. It can easily be inferredthat any particular embodiment illustrated with diagrams and explainedcannot be considered limiting. For example the metallization layer 420may include multiple layers sandwiched between multiple insulatinglayers 422 connecting multiple devices and/or multiple chips on thesubstrate.

Referring to FIG. 4 g-1 and FIG. 4 g-2 there is shown a next stepdetailing a post micro/nano fabrication step after the integration torealize released mechanical structures 421. The third insulation layer422 may provide a protective layer for the ensuing fabrication. In thedetailed embodiment the insulating layers are patterned and etched tocreate an opening 424 on the substrate 402. The opening 424 may beformed by anisotropic etching. The mechanical structural layers of theMEMS/NEMS 404 can be released using an isotropic etch forming a cavity426. The cavity 426 defines a sandwiched suspended structure 428.

In a next step as shown in FIG. 4 g-3, the packaging of the integrateddevice is detailed. The packaging of the device may include aligning arigid substrate 430 and bonding it to the substrate 402 by using aninterfacial material 432. The packaging substrate 430 may be selectedfrom ceramics, thermoplastics, thermosets, glass, silicon, quartz,plastic or metals. The bonding may be anodic, eutectic, solder, polymeror fusion bonding. The interfacial material 432 may be selected frommetal and/or alloys like gold, tin, epoxies like Benzocyclobuten (BCB)and SU8.

In a subsequent step as shown in FIG. 4 g-4, a secondary protectivelayer 434 may be applied overlying the rigid substrate 430. Thesecondary protective layer 434 may be selected from polymers, oxides,nitrides, metals or a combination of them. A person of ordinary skill inthis art will be able to easily make further alterations andmodifications in packaging after reading the present invention.

Referring to FIG. 4 h-1 to FIG. 4 h-3 there is shown an alternativeembodiment of the post micro/nano fabrication step after the integrationto realize released mechanical structures. The third insulation layer422 may provide a protective layer for the ensuing fabrication. In thedetailed embodiment, the backside of the substrate 402 is etchedindicated by 436 and shown in FIG. 4 h-1. In the ensuing fabrication theinsulating layers may be patterned and etched to create several openings436 on the substrate 402. The openings 436 may be formed by anisotropicetching. The mechanical structural layers of the MEMS/NEMS 404 can bereleased using another anisotropic etch shown in FIG. 4 h-3, forming afree standing and or suspended structure 438.

In a next step as shown in FIG. 4 h-4, the packaging of the integrateddevice is detailed. The packaging of the device may include aligning arigid substrate 430 and bonding it to the substrate 402 by using aninterfacial material 432. The packaging substrate 430 may be selectedfrom ceramics, thermoplastics, thermosets, glass, silicon, quartz,plastic or metals. The bonding may be anodic, eutectic, solder, polymeror fusion bonding. The interfacial material 445 may be selected frommetal and/or alloys like gold, tin, epoxies like Benzocyclobuten (BCB)and SU8.

In a subsequent step as shown in FIG. 4 h-5, a secondary protectivelayer 434 may be applied overlying the rigid substrate 430. Thesecondary protective layer 434 may be selected from polymers, oxides,nitrides, metals or a combination of them. A person of ordinary skill inthis art will be able to easily make further alterations andmodifications in packaging after reading the present invention.

Referring to FIGS. 5 a-f there is shown another alternative embodimentin which opening and trench in the semiconductor substrate may be usedinterchangeably. FIG. 5 illustrates a cross-sectional process flow for amonolithic hybrid integrated piezoresistive strain gage on a substrate502.

Referring to FIG. 5 a there is shown a first step including providing asilicon substrate 502. In this embodiment, a first insulating layer 505may be a thermal silicon-dioxide deposited on the silicon substrate 502.The average thickness of the insulating layer may be about 0.54 microns.This is followed by the deposition of 0.5 microns of Low stresspolysilicon 506 or structural layer which may be later boron doped andannealed to define the conductive sensing area. The first insulatinglayer 505 and the polysilicon layer 506 or structural layer arepatterned to define the MEMS sensing area 504 which in this specificembodiment is the polysilicon piezoresistive sensing area.

Next, as shown in FIG. 5 b, a photo-resistive protective layer 508 maybe applied to the semiconductor substrate 502 by either spin coating ordepositing in vacuum to protect the MEMS/NEMS area 504 from furtherprocessing steps. Protective layer 508 may also be selected from oxides,nitrides, polymers, or their combination having a thickness ofsub-microns to several microns which can effectively protect theelectronics. The protective layer 508 may be selectively patterned usinglithography to define an opening 510 in close proximity and outside ofthe MEMS/NEMS area 504. The trench 510 may be etched using DRIE Boschprocess and may be lithographically defined by the size of theinstrumentation amplifier chips 514. The protective layer 508 may thenbe removed.

In a following step, as shown in FIG. 5 c, a filler layer 512 may bedeposited or dispensed into the trench 510 to anchor the chip 514 intothe cavity and also to fill a gap between the chip 514 and the wall ofthe trench 510 and will also ensure the planarity of the chip 514 to thesubstrate 502. The filler material 512 may be selected from oxides,polyimides, silicones, epoxies, or their combination or any othermaterials with similar properties.

In a next step as shown in FIG. 5 d, the chip or instrumentationamplifier die 514, is placed in the trench 510. In another aspect, thechip or die 514 may include, a CMOS integrated chip, voltagecomparators, diodes, op-amps, or other electronic components such aspower management circuits, resistors, capacitors, and inductors. The die514 may also include MEMS/NEMS dies such as: accelerometers, resonators,micro-gyroscopes, microphones, micro-bolometers, transducers involvingchemical and biological, optical, mechanical, radiation, thermal,capacitive, rotation, strain, magnetic and electromagnetic, flow, andmicro-fluidic chemical properties of liquids and gases. It should berealized that various other MEMS/NEMS dies may also be included.

In a following step as shown in FIG. 5 e, a planarization layer 516 maybe deposited covering the front face and/or the sides of the chip 514providing continuity from the semiconductor substrate 502 to the chip514. In one aspect, the planarization layer 516 may be parylene.Alternatively the planarization layer 516 may be selected from polymers,oxides, nitrides, glass, quartz polyimide, and silicone.

In a next step as shown in FIG. 5 e, a metallization layer 520 such asTi/Au may be applied by e-beam evaporation and electroplated to connectthe MEMS/NEMS on the semiconductor substrate 502 to the chip 514 whichincludes a contact area having an input/output pad or bond area to makeelectrical contact. Alternatively, the metallization layer 520 may beselected from metals such as, aluminum, copper, titanium, chrome, gold,silver, iridium or their combination that can be evaporated, sputteredor electroplated. A second insulating layer 522 may be depositedoverlying the MEMS/NEMS on the semiconductor substrate 502, overlyingthe metallization layer 520 on the chip 514. The second insulation layer522 may be selected from polymers including polyimide, silicones,oxides, nitrides, glass, quartz or their combination. In one aspect, anopening 524 on the substrate 502 may be formed to create a standingstructure. The opening 524 may be formed by anisotropic etching. Aperson of ordinary skill in this art will be able to easily make furtheralterations and modifications in packaging after reading the presentinvention. It can easily be inferred that any particular embodimentillustrated with diagrams and explained cannot be considered limiting.For example the metallization layer 520 may include multiple layerssandwiched between multiple insulating layers 522 connecting multipledevices and/or multiple chips on the substrate.

Referring to FIG. 6-9 there is shown an example of monolithic hybridintegration of a micro-machined polysilicon piezoresistive strain gage600 integrated with an amplifier AD621 die 514. A first insulating layer505 of thermal silicon-dioxide may be deposited on the silicon substrate502. The average thickness measured using a Nanospec was 0.54 microns.This is followed by the deposition of 0.5 microns of Low stresspolysilicon 506 which is later boron doped and annealed. The polysilicon506 is first patterned defining the dimensions of piezoresistors 702.This is followed by patterning the thermal oxide 505 below to define anopening or trench 510 in the silicon substrate to place the amplifierdie 514 with the dimensions of the pattern proportional to the lengthand breadth of the amplifier die 514. The patterned area of thepolysilicon 506 and the thermal silicon-dioxide 505 define the MEMS area504. Alternatively, micro-machined micromechanical systems having hightemperature materials including but not limited to LPCVD oxide, nitrideand polysilicon may be used to effectively fabricate transducersincluding but not limited to accelerometers, resonators,micro-gyroscopes, microphones, micro-bolometers, etc. A Photoresistprotective layer 508 may be coated on the MEMS device area 504 on thesubstrate 502 to protect them from further fabrication steps that willbe carried out on the same substrate 502. This protective layer ispatterned to protect the MEMS device area from the ensuing chemicaletching and defining the opening 510 in the silicon semiconductorsubstrate 502. The AD621 amplifier die 514 may be placed in the opening510 which may be a photolithographically etched trench with a fillermaterial 512. Next, the die 514 may be connected to the alreadyfabricated portion of the MEMS/NEMS device area 504 with a metallizationlayer 520. The CMOS or electronic dies may also include moresophisticated circuits such as digital interfaces and micro controllers.FIG. 9 shows the data from testing the above embodiment. The testingsetup involved wire bonding the output pads 800, shown in FIG. 8 to aPrinted Circuit Board which was then mounted onto a Bread board forexternal connections. The only equipment required for the initialtesting was the use of a Power supply and a Digital Multimeter. The MEMSpiezoresistive Wheatstone bridge network 504 was connected to the inputsof the Ad621, 514 instrumentation amplifier using evaporated metaltraces 520. These metal traces 520 not only ensured the output from theinstrumentation amplifier but also set the gain of the amplifier to 100by connecting the RG1 and RG8 pins on the chip 514 shown in FIG. 6. Anexternal voltage stimuli was applied to the electronics chip 514simultaneously powering the MEMS wheatstone network and the outputrecorded on the Digital Multimeter. This test was performed without anystresses applied.

In one aspect of integration, the processing temperature of the processfor the CMOS component is below 400° C. to protect the aluminum in theelectronics while other steps may have temperatures below or above thisrange without affecting the CMOS thereby defining a temperatureindependent process and the use of temperature independent materials,which has been a limiting step in prior art integration methodologiesthat is overcome with the present invention. For example, theapplication of the polysilicon material may be performed at a hightemperature above 1000 degrees centigrade and will not destroy thecomponent being produced. The process may also include protecting theMEMS device area by protecting the CMOS and or MEMS/NEMS chip areas andthe MEMS/NEMS device area to realize a released mechanical structurallayer or other structures depending on a specific application.

In an alternative embodiment as shown in FIG. 10 pre-fabricatedMEMS/NEMS high temperature materials including but not limited to LPCVDoxide, nitride and polysilicon is used as the starting material on adouble sided semiconductor substrate with through substrate conductivevias to effectively fabricate transducers including but not limited toaccelerometers, resonators, micro-gyroscopes, microphones,micro-bolometers, etc. In FIG. 10 a, 1006 represents LPCVD polyisliconmaterial with a thickness ranging from a few angstroms to tens ofmicrons and 1003 represents a second layer of conductive layer includingbut not limited to polysilicon, metallization, etc. A protective layermay be coated on the MEMS device area on the substrate to protect themfrom further fabrication steps that will be carried out on the samesubstrate. This protective layer protects the MEMS device area from theensuing chemical etching. The CMOS electronics dies or any otherMEMS/NEMS chips may be placed in a photo lithographically etched trenchon the backside of the semiconductor substrate with the help of a fillermaterial and then connected to the already fabricated portion of theMEMS/NEMS device area with metallization evaporated or sputteredinterfacing the through substrate conductive vias. The CMOS orelectronic dies also involve more sophisticated circuits includingdigital interfaces and micro controllers. Thus the temperaturelimitation of the process to below 400° C. to protect the aluminum inthe electronics, which has been the limiting step in some of the currentintegration methodologies, can now be overcome with the presentinvention with the potential to realize several novel devices. Thisinvention will also simplify the use of sensing arrays and shrinking thefinal sensing system. Processing can further resume on the MEMS devicearea by protecting the CMOS and or MEMS/NEMS chip areas and theMEMS/NEMS device area to realize a released structural layer and anyother requirement depending on a specific application. It should berealized that a person of ordinary skill in this art will be able tomake further alterations and modifications.

Referring to FIG. 10 a there is shown a first step including providing adouble sided substrate 1001. The semiconductor substrate may include afront side 1000 and the backside 1001 and may include MEMS/NEMSmaterials 1004 applied thereon on front side 1000. In one aspect, thestructural MEMS/NEMS material 1004 that can be made conductive includehigh temperature MEMS materials such as LPCVD polysilicon 1006 that canbe later doped in boron or phosphorous and or may also include LPCVDnitride and or metals 1003 such as aluminum, copper, titanium, chrome,gold, silver, iridium or their combination that can be evaporated,sputtered or electroplated and sacrificial layers 1005 The metallization1003 is electrically connected to through substrate conductive vias1002.

Next, as shown in FIG. 10 b, the trench 1008 may be etched using DRIEBosch process and may be lithographically defined by the size of chips1012. In a following step, a filler material 1010 may be deposited ordispensed into the trench 1008 to anchor the chip 1012 into the cavityand also to fill a gap between the chip 1012 and the wall of the trench1008 and will also ensure the planarity of the chip 1012 to thesubstrate 1001. The filler material 1010 may be selected from oxides,polyimides, silicones, epoxies, or their combination or any othermaterials with similar properties.

In a next step as shown in FIG. 10 c, the chip 1012 of CMOS, MEMS/NEMSor a combination of them may be placed in the at least one trench 1008.As described above, a CMOS integrated chip may include voltagecomparators, diodes, op-amps, or other electronic components like powermanagement circuits, resistors, capacitors, and inductors. A MEMS/NEMSdies may include but are not limited to accelerometers, resonators,micro-gyroscopes, microphones, micro-bolometers, transducers involvingchemical and biological, optical, mechanical, radiation, thermal,capacitive, rotation, strain, magnetic and electromagnetic, flow, andmicro-fluidic chemical properties of liquids and gases.

In a following step as shown in FIG. 10 c, a planarization layer 1014may be deposited covering the front face and/or the sides of the chip1012 providing the continuity from the semiconductor substrate 1001 andfiller material 1010 to the chip 1012. The planarization layer 1014 maybe selected from polymers, oxides, nitrides, glass, quartz polyimide,parylene, silicone, or a combination of the above.

In a next step as shown in FIG. 10 d, a metallization layer 1022 may beapplied to connect the MEMS/NEMS on the semiconductor substrate 1000after patterning the planarization layer 1014 to the cmos chip 1012 thatis present on the side 1001 with the electrical connection made usingthrough substrate vias 1002. A post micro/nano fabrication step isperformed by etching away the sacrificial layer 1005 on the MEMS/NEMSsurface 1000 to release the structural layer 1006. A person of ordinaryskill in this art will be able to easily make further alterations andmodifications in packaging after reading the present invention. It caneasily be inferred that any particular embodiment illustrated withdiagrams and explained cannot be considered limiting. For example themetallization layer 1022 may include multiple layers connecting multipledevices and/or multiple chips on the substrate.

In an alternative embodiment as shown in FIG. 11, pre-fabricatedMEMS/NEMS chips are integrated into already post cmos 1104 circuits withthrough substrate vias 1103. The semiconductor substrate may include afront side 1100 and the backside 1101. In a following step as shown inFIG. 11 b a trench 1108 may be etched using DRIE Bosch process and maybe lithographically defined by the size of chips 1112. In a followingstep, a filler material 1110 may be deposited or dispensed into thetrench 1108 to anchor the chip 1112 into the cavity and also to fill agap between the chip 1112 and the wall of the trench 1108 and will alsoensure the planarity of the chip 1112 to the substrate 1101. The fillermaterial 1110 may be selected from oxides, polyimides, silicones,epoxies, or their combination or any other materials with similarproperties.

In a next step as shown in FIG. 11 c, the chip 1112 of CMOS, MEMS/NEMSor a combination of them may be placed in the at least one trench 1008.As described above, a CMOS integrated chip may include voltagecomparators, diodes, op-amps, or other electronic components like powermanagement circuits, resistors, capacitors, and inductors. A MEMS/NEMSdies may include pre-fabricated structural material 1116 and dielectriclayers and include but are not limited to accelerometers, resonators,micro-gyroscopes, microphones, micro-bolometers, transducers involvingchemical and biological, optical, mechanical, radiation, thermal,capacitive, rotation, strain, magnetic and electromagnetic, flow, andmicro-fluidic chemical properties of liquids and gases.

Referring to FIG. 11 c, a planarization layer 1114 may be depositedcovering the front face and/or the sides of the chip 1112 providing thecontinuity from the semiconductor substrate 1101 and filler material1110 to the chip 1112. The planarization layer 1114 may be selected frompolymers, oxides, nitrides, glass, quartz polyimide, parylene, silicone,or a combination of the above.

In a next step as shown in FIG. 11 d, a metallization layer 1122 may beapplied to connect the cmos on the semiconductor substrate 1100 afterpatterning the planarization layer 1114 to the cmos, mems/nems chip 1112that is present on the side 1101 with the electrical connection madeusing through substrate vias 1102. A post micro/nano fabrication step isperformed by etching away the dielectric layer on the MEMS/NEMS chip1112 to release the structural layer 1116. A protective cap 1124 isfinally laced on the integrated system on the semiconductor substrateside 1101 to protect the mems/nems structural moving part 1116. A personof ordinary skill in this art will be able to easily make furtheralterations and modifications in packaging after reading the presentinvention. It can easily be inferred that any particular embodimentillustrated with diagrams and explained cannot be considered limiting.For example the metallization layer 1122 may include multiple layersconnecting multiple devices and/or multiple chips on the substrate.

While the above examples provide a description of the process of thepresent invention, they should not be read as limiting the process ofthe present invention. The invention has been described in anillustrative manner. It is to be understood that the terminology whichhas been used is intended to be in the nature of words of descriptionrather than limitation. Many modifications and variations of theinvention are possible in light of the above teachings. Therefore,within the scope of the appended claims, the invention may be practicedother than as specifically described.

1. A method of forming a Monolithic CMOS-MEMS hybrid integrated,packaged device comprising the steps of: providing a semiconductorsubstrate selected from pre fabricated CMOS circuits, MEMS and NEMSmaterials on a front side and a polished backside area available forpost-CMOS, micro/nano fabrication with through substrate conductive viasand the prefabricated MEMS or NEMS materials having conductivestructural and dielectric layers; forming at least one opening in thepolished backside of the semiconductor substrate including protectingthe front-side; applying at least one filler material in the at leastone opening on the semiconductor substrate; positioning at least oneprefabricated MEMS, NEMS or CMOS chip on the filler material, the chipincluding a front face and a bare back face with the filler materialenabling planarization of all the corners of the chip to the substrate;forming at least one metallization layer connecting the throughsubstrate conductive vias to the at least one chip; performing at leastone micro/nano fabrication etching step to release the MEMS/NEMSstructural layer on the front side.
 2. The method of claim 1, whereinthe MEMS/NEMS materials include structures selected from:accelerometers, resonators, micro-gyroscopes, microphones,micro-bolometers, transducers involving chemical and biologicalproperties, optical sensors, mechanical sensors, radiation sensors,thermal sensors, capacitive sensors, rotation sensors, strain sensors,magnetic and electromagnetic sensors, flow sensors, and sensors formicro-fluidic chemical properties of liquids and gases.
 3. The method ofclaim 1, wherein the structural layer comprises polysilicon with theportion of the conductive area being doped and annealed.
 4. The methodof claim 1, wherein the opening in the semiconductor substrate is formedby etching with Deep Reactive Ion Etching (DRIE).
 5. The method of claim1, wherein the filler layer is selected from epoxies, polyimides, SU8,and polymers.
 6. The method of claim 1, wherein the at least one chip isselected from: CMOS integrated circuits, electronics, amplifier dies,analog to digital converters.
 7. The method of claim 1, wherein themetallization layer is selected from aluminum, titanium, chrome, gold orplatinum or a combination of the same that can be evaporated, sputteredor electroplated.
 8. The method of claim 1, wherein the micro/nanofabrication etching step is selected from wet, dry, isotropic, andanisotropic etching.
 9. A method of forming Monolithic CMOS-MEMS hybridintegrated, packaged device comprising the steps of: providing asemiconductor substrate with pre-fabricated CMOS circuits on a frontside and a polished back-side with through substrate conductive vias;forming at least one opening in the polished backside of thesemiconductor substrate including protecting the front-side; applying atleast one filler material in the at least one opening on thesemiconductor substrate; positioning at least one MEMS, NEMS chips withpre-fabricated structural and dielectric layers or CMOS chips on thefiller material, the chip including a front face and a bare back facewith the filler material enabling planarization of all the corners ofthe chip to the substrate; forming at least one metallization layerconnecting the through substrate conductive vias to the at least onechip; performing at least one micro/nano fabrication etching step torelease the structural on the prefabricated MEMS/NEMS chips; positioninga protective cap to package the integrated device over the MEMS/NEMSdevice area on the pre-fabricated chips.
 10. The method of claim 9,wherein the opening in the semiconductor substrate is formed by etchingwith Deep Reactive Ion Etching (DRIE).
 11. The method of claim 9,wherein the structural layer comprises polysilicon with the portion ofthe conductive area being doped and annealed.
 12. The method of claim 9,wherein the planarization layer is selected from oxides, nitrides,glass, quartz, and polymers.
 13. The method of claim 9, wherein theprefabricated chip is selected from: CMOS integrated circuits,electronics, amplifiers, and Analog to Digital converters.
 14. Themethod of claim 9 wherein the MEMS/NEMS materials include structuresselected from: accelerometers, resonators, micro-gyroscopes,microphones, micro-bolometers, transducers involving chemical andbiological properties, optical sensors, mechanical sensors, radiationsensors, thermal sensors, capacitive sensors, rotation sensors, strainsensors, magnetic and electromagnetic sensors, flow sensors, and sensorsfor micro-fluidic chemical properties of liquids and gases.
 15. Themethod of claim 9, wherein the metallization layer is selected fromaluminum, titanium, chrome, gold or platinum or a combination of thesame that can be evaporated, sputtered or electroplated.